Diamine salts useful for inhibiting the corrosion in return steam condensate lines



United States Patent 4 Claims. c1. 266-50117) The subject application isa divisional application of my copending application Ser. No. 583,397which was filed on May 10, 1956.

This invention relates to novel compounds which are useful in inhibitingcorrosion in return steam condensate lines. More particularly, thesubject invention is directed to new compositions of matter which areorganic acid salts of the reaction product of an alkylene oxide and asubstituted alkylene diamine.

It is well known that steam lines and steam condensate lines are subjectto corrosion which is very difficult to control. This corrosion isapparently due, to a large extent, to carbon dioxide and oxygen in theboiler-steamcondeusate system. Carryover from the boiler water can alsoincrease the corrosion. The problem of corrosion of the internalsurfaces of steam condensate return lines has been recognized for manyyears. Generally, the difficulties that have been experienced arepitting, grooving and ultimate deterioration of sections of thecondensate return system and the plugging of constrictions in the systemwith the insoluble products of corrosion. To evaluate properly theactual cost of return line corrosion, it is necessary not only toconsider the loss in terms of labor, curtailed production and the costof the material destroyed, but also to weigh effects in terms ofinelficient operation of fouled equipment.

Experimental studies by various investigators indicate that dissolvedcarbon dioxide and oxygen are responsible for practically all thecorrosion in the condensate lines. The various expedients that have beendevised for combating this attack are as follows:

(1) The use of corrosion resistant alloys, which is generallyprohibitive from a cost standpoint.

(2) Minimizing the amount of carbon dioxide and oxygen in the condensateeither by venting or pretreatment of the boiler feedwater.

(3) Chemical treatment of the condensate.

It is known to use a readily volatile alkaline amine material forprotection against corrosion in steam and return condensate lines butthe results obtained with such amines have sometimes left much to bedesired, particularly in steam and condensate systems of great length orin tall buildings. Moreover, these amines to be effective, are usuallyrequired in amounts which are roughly pro- \portional to the carbondioxide content of the condensate. Where the return of condensate to theboiler constitutes a minor fraction of the boiler feed, such treatmentoften becomes economically impractical.

Where high pressure steam is required to operate industrial devices,such as turbines, it has been the experience of the art that certaintreating agents will undergo decomposition and form deposits on thesurfaces of the devices which, in many instances, will necessitatecostly shutdowns and repairs.

It would be desirable to have a chemical treatment capable of beingapplied to any part of a steam or condensate return system at small,economical dosages and have beneficial results obtained in all cases.

The principal object of the present invention is to provide compositionsof matter for the treatment of steam condensates which produce improvedresults in preventing or minimizing corrosion in steam lines, traps,condensers, valves, and in other parts of steam systems such as turbineblades.

It has been found that the corrosion in steam and condensate returnsystems may be prevented or substantially mitigated by treating suchsystems with a corrosion inhibiting amount of a carboxylic acid salt ofthe reaction product of a low molecular weight alkylene oxide and asubstituted alkylene diamine. These materials are effective when addedeither to the boiler feedwater, to the steam lines, or to the condensatereturn lines. When added to the boiler feedwater it is generallynecessary to add a slightly excessive amount to insure that enough ofthe chemical steam distills into the steam and condensate returnsystems. Generally, however, it is preferred to add the treatment to thesteam condensate line since it is this part of the system wherecorrosive attack is the severest and the smallest amounts of thetreatment are the most effective. From a practical standpoint, thechemical is most conveniently applied to the boiler feedwater.

The amount of treatment should be at least 1 part per million of thecorrosion inhibiting chemical by weight of the steam or steamcondensate, preferably 2 to 5 parts per million and even more preferably10 to 25 parts per million. The dosage will, of course, vary dependingon the conditions of the system and other variable factors and hence,dosages as high as to parts per million may be necessary underextraordinarily corrosive conditions.

The employment of the corrosion inhibiting chemicals in accordance withthis invention is applicable to the generation of steam at varioustemperatures and pressures. Good results can be obtained where steam isgenerated under atmospheric conditions, subatmospheric conditions orsuperatmospheric conditions. In most cases, steam is generated atpressures from atmospheric up to 1500 pounds per square inch or more andthe corresponding temperatures.

The substituted alkylene diamines which are used as starting materialsin preparing the compositions useful in the practice of the inventionhave the following general formula:

wherein R is an acyclic hydrocarbon radical containing from 10 to 32carbon atoms and n is an integer from 2 to 6.

The radical R is conveniently derived from a saturated or unsaturatedfatty group. Such groups as dodecyl, tetradecyl, hexadecyl, octadecyl,octadecenyl, and octadecadienyl may be substituents with good resultsbeing obtained in each instance. Extremely good results are affordedwhen R is a mixture of alkyl radicals such as are found in vegetableoils and animal fats. Coco, soya and tallow are examples of such mixednatural radicals.

The diarnine portion of the compounds described above may be one of anynumber of the known diamines. Ethylene diarnine, 1,2 propylene diamine,1,3 propylene diamine and hexamethylene diamine are several examples.

The substituted alkylene diamines may be prepared by several difierenttechniques. For instance, the alkylene diamines may be alkylated with analkyl halide to produce the desired product. Such a method isillustrated in Kyrides US. Patent 2,246,524. Another method is to reactan alkylamine with acrylonitrile and then hydrogenate whereby an alkylsubstituted propylene diamine is produced. Commerically availableN-alkyl propylene diamines are the products manufactured by the ArmourChemical Division under the trade name, Duomeens.

Specific Duomeens are N-lauryl propylene diamine; N- coco propylenediamine; N-soya'propylene diamine, and N-tallow propylene diamine.

The substituted alkylene diamines thus described are capable of beingreacted with varying amounts of several of the well known low molecularweight alkylene oxides, such as ethylene oxide, 1,2-propylene oxide,butylene oxide or the like, to produce products varying in theirphysical and chemical properties. To be suitable for present purposes,the hydroxyalkylated, substituted alkylene diamines must be waterdispersible to the extent that 5% by weight or more forms a uniformdispersion in aqueous media. This is usually accomplished byhydroxyalkylating 1 mol of diamine with 1 to 4, and preferably 2-3, molsof ethylene oxide or other alkylene oxide to produce the degree of waterdispersibility desired.

The hydroxyalkylation of the products may be performed by any one ofseveral well known methods. Since there are three reactive hydrogenatoms in the alkyl substituted diamines the hydroxyalkylation couldconceiva'bly take place at any of the sites. Hence, one mol of analkylene oxide could react with any one of the three hydrogen atoms toproduce a mixture of hydroxyalkylated products. Several of thesereaction products are The salt forming aliphatic carboxylic acids shouldnot exceed carbon atoms in chain length. For purpose of classificationthe acids may be divided into four classes:

(I) Aliphatic monocarboxylic acids (II) Aliphatic dicarboxylic acids(III) Hydroxy substituted carboxylic acids (IV) Hydroxy substitutedpolycarboxylic acids In class I such acids as acetic, propionic,n-butyric, isobutyric, n-heptylic, caprylic and prelargonic acids may beused. Examples of class II are oxalic, malonic, succinic, glutaric,adipic, pimelic, suberic, azelaic and sebacic acids. Glycolic, gluconic,glyceric and lactic acids are illustrative of class III. Class IV wouldinclude such acids as malic and citric.

For purposes of illustration, several aliphatic carboxylic acid salts ofthe alkyl substituted propylene di-amines listed in Table I are shownbelow in Table II.

TABLE II Composition Composition Aliphatic Mol Ratio Number NumberOarboxylic Reaction Table I Acid ProductzAcid I Acetic acid 1:1

I Lactic acid 1:1

I Citric acid 1:1

III Butyric acid 1:1

IV Malic acid... 1:1

V Succim'c acid 1:1

I Malonic acid 2:1

I Adipic acid. 1:1

The salts listed in Table II were prepared by heating the compositionsin Table I, which ranged from viscous liquids to pastes, and adding theacid, with continued heat, until a homogeneous product was produced.

When boiler feedwater applications are contemplated it is sometimeshelpful to formulate the compositions of the invention with boilerantifoams. The compositions of the invention will not produce foaming orpriming when used at the concentrations recommended herein, but in theevent high concentrations occur in the boiler water, the use ofantifoams is a safeguard to insure good operation of the boiler.Antifoams that may be used are those described in US. Patents 2,575,298,2,626,243, 2,575,276, 2,609,344 and 2,717,881. Only a few parts permillion of these antifoams in the boiler water are required to insureagainst any harmful foaming.

EVALUATION OF THE INVENTION (A) Screening tests.The material to betested was added, at a concentration of parts per million, to 350 ml. ofdeionized water contained in a 400 ml. beaker. The beaker was held in anoil bath at a temperature of about F. The solution was stirred at about1750 rpm. with centrifugal-type glass stirrers. A mixture of CO and airwas bubbled through the solution during the test. A mild steel specimenwas sandblasted, weighed, and placed in the solution overnight. Theweight loss of the specimen was then determined. A similar test, calledthe blank, was made under identical conditions except that no corrosioninhibitor was added to the water. The data from these screening testsare presented in Table III as percent protection compared with the blanktest.

TABLE III Composition: Percent protection Composition IX, Table II 93Sebacic acid 11 Sodium hexametaphosphate 19 Octadecyl urea 0 From theabove it is evident the compositions of the invention provided superiorcorrosion protection as against the poor or slight protection affordedby other inhibitors tested.

(B) Experimental condensate corrosion tests.This series of corrosiontests were made in an apparatus designed to simulate a severelycorrosive condition which might be encountered in a steam condensatesystem. In this apparatus a synthetic condensate was produced ina glasstower by aerating heated distilled water with a mixture of carbondioxide and air. This condensate and a solution of the treating chemicalwere proportioned into a test container by gravity feed. A number ofsteel test coupons were suspended in the latter and the liquid wasmildly agitated with a paddle stirrer. At periodic intervals a testspecimen was removed from the bath and the weight loss determined. Thetemperature, free carbon dioxide and dissolved oxygen of the syntheticcondensate, and the treatment concentration were controlled throughoutthe test.

The corrosion test specimens consisted of 1 inch x 2 inch panels whichwere sheared from a single sheet of 22 gauge cold rolled mild steel. Allspecimens were uniformly sandblasted before being immersed in the bath.

Agitation of the liquid was initiated and the water in the bath washeated to and thermostatically controlled at i1 F. The free carbondioxide and dissolved oxygen of the water were maintained at 45 14 partsper million and 3.5 1 10.2 parts per million, respectively.

A complete, detailed description of the test apparatus and method isdescribed in the article, A Laboratory Method for the Study of SteamCondensate Corrosion Inhibitors, by H. I. Patzelt, Corrosion, January1953.

The following examples illustrate the results obtained in the evaluationof test specimens using treating chemicals within the scope of theinvention.

Example I In this series the two compositions, composition VIII, TableII and composition IX, Table II were each tested separately at 10 partsper million. At the end of the 6th day the weight losses were 221 and121 milligrams, respectively.

The corrosive conditions maintained in these tests when compared withmost industrial condensate return systems are extremely severe.Inhibitors giving only good to fair results in the test in most casesgive outstanding results in actual use at lower dosages.

(C) Effect'on brass.-The screening test method (A above) was used, Brassspecimens in place of the steel were suspended in deionized water.Rather than running a percent comparison against the blank, weightlosses in milligrams were determined. Composition XVI showed a weightloss of only 13.2 milligrams.

Example II This test was conducted in an actual boiler system todetermine whether composition XVI would be detrimental to normal boileroperation. The test boiler generated a total of 800,000 to 1,000,000pounds of steam per day at 125 pounds per inch. Composition XVI was fedby dispersing 1 gallon into 30 to 40 gallons of condensate return andinjecting it directly into the steam header. The dosage for the entiretest period was maintained at parts per million of the steam.

A by-pass corrosion test loop was installed in front of one of thecondensatereturn pumps. This loop was approximately 3,000 feet from theboiler and 400 to 700 gallons passed through per day. The specimen was a1 inch pipe nipple which was placed in the system with appropriatefittings.

The test was run for one month at the end of which time inspectionrevealed corrosion rates of the specimen were being satisfactorilycontrolled. A sample of condensate was collected from the by-pass loopand analysis showed it to contain 2.0:06 parts per million ofcomposition XVI. Of interest is the fact that the sample thus taken wasat a point most remote from the boiler. There was no evidence ofdeposits forming in the system and no unusual foaming occurred in theboiler.

The expression water dispersible as used herein means a material whichin water or other aqueous media does not form a true solution yet it iscapable of remaining in a suspended condition at the concentrationsherein specified for relatively long periods of time. These suspensionsmay or may not be colloidal.

I claim:

1. Salts of an aliphatic carboxylic acid and salts of the reactionproduct of 3 mols of ethylene oxide per mol of a substituted alkylenediamine of the formula RNCH2CH2-CH2NH wherein R is a long chain acyclichydrocarbon radical 5 containing 10 to 32 carbon atoms, the saltforming, aliphatic carboxylic acid being selected from the groupconsisting of acetic, propionic, n-butyric, isobutyric, nheptyl'ic,caprylic, pelargonic, oxalic, malonic, succinic, glutaric, adipic,pimelic, suberic, azelaic, sebacic, glycolic, gluconic, glyceric,lactic, malic and citric.

l0 2. The acetic acid salt of the reaction product of ethylene oxide andN-tallow propylene diamine in 9. mol ratio of about 3 mols'of ethyleneoxide per mol of said diamine.

3. The lactic acid salt of the reaction product of ethylene oxide andN-tallow propylene diamine in a mol ratio of about 3 mols of ethyleneoxide per mol of said diamine.

4. The citric acid salt of the reaction product of ethylene oxide andN-tallow propylene diamine in a mol ratio of about 3 mols of ethyleneoxide per mol of said diamine.

References Cited UNITED STATES PATENTS 2,243,329 5/1941 De Groote 2605832,701,239 2/1955 Ryznar 260584 2,739,980 3/1956 Chester 260501 2,759,0218/1956 Gaar et a1 260584 2,920,040 1/1960 Jolly 260-501 n 2,552,5315/1951 De Groote 260501 2,868,833 1/1959 Szabo et al. 260-501 2,914,55711/1959 Oxford 260-501 2,995,603 8/1961 Hutchison 260--501 3,029,1254/1962 Hummel 212.7

2,143,388 1/1939 Schlock 260501 2,736,658 2/1956 Pfohl et a1. 2605012,952,707 9/1960 Nikawitz 260501 X 2,930,761 3/ 1960 Charret 260584 X 40OTHER REFERENCES Industrial and Engineering Chemistry, vol. 41, No. 10,October 1949, pp. 20802090.

LEON ZITVER, Examiner.

LORRAINE A. WEINBERGER, Primary Examiner.

M. B. WEBSTER, B. EISEN, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,378,581 April 16, 1968 Louis E. Hummel It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 3, line 46, "prelargonic" should read pelargonic Column 5, line44, after "and" cancel "salts". Column 6, line 34, "Schlock" should readSchlack Signed and sealed this 25th day of November 1969.

(SEAL) Attest:

Edward M'Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

1. SALTS OF AN ALIPHATIC CARBOXYLIC ACID AND SALTS O THE REACTIONPRODUCT OF 3 MOLS OF ETHYLENE OXIDE PER MOL OF A SUBSTITUTED ALKYLENEDIAMINE OF THE FORMULA